The present invention relates to a positioning system and, particularly, to a control method and apparatus for a fast and accurate positioning system using a stepper motor. More particularly, this invention relates to a control method and apparatus for positioning a magnetic head to a target track on a magnetic recording disc or floppy disc accurately and rapidly by employment of a stepper motor.
Many of modern compact magnetic disc drive units and floppy disc drive units employ a stepper motor in their head positioning system. The stepper motor positioning system is less expensive than the positioning system using a voice coil motor, while on the other hand its head positioning accuracy is inferior due to variation in characteristics such as hysteresis of the stepper motor, making it difficult to increase the track density of the recording disc.
The applicant of this invention noticed that the aforementioned variation in such characteristics as hysteresis are closely related to the assembling accuracy of the stepper motor stator poles, and proposed a head positioning system removing the positioning error by positioning the head by driving the stepper motor by an integral multiple of the number of the stationary windings. (Refer to U.S. Pat. No. 4,490,662.) Although this technique alleviates the positioning error successfully, the time length needed for each positioning operation is left unconsidered. Reference may also be made to U.S. Pat. No. 4,489,259 by White et al.